Photographic transfer product and process



April 14, 1953 E. LAND 2,635,048

PHOTQGRAPHIC TRANSFER PRODUCT AND PROCESS Eilad July 6, 194a Suppor'r Phoiosensifivc Silver Halide Layer lob Processing L q l Siabilizing Agcni |2b |2a Silver Precipiiqfion lnificnor Supporf INVENTOR EDWIN H. LAND ATTORNEY Patented Apr. 14, 1953 2,635,048 PHOTOGRAPHIC TRANSFER rnonuo'r I AND rnocnss Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass; a cor poration of Delaware Application July s, 1948, Serial mime This invention relates to photographic processes involving the development of photosensitive silver halide emulsions, and to products useful in the performance of said processes.

It has been proposed to carry out the processing of a photosensitive element comprising a silver halide emulsion layer by distributing a predetermined quantity of processing liquid uniformly over the area of the photosensitive element to be processed in a'position to permeate the photosensitive layer. This distribution of the processing liquid may be obtained by doctoring, roll coating or otherwise applying the same directly to the surface of the photosensitive element, or by first distributing the processing liquid on or in the surface portion of another element which is thereafter brought into face-to-face engagement with the photosensitive element, and is 7 preferably accomplished by spreading the liquid between the photosensitive element and another element. Processes of this type are characterized by the fact that the processing liquid which is distributed layerwise constitutes the sole source of liquid for the processing operation.

In the processes comprehended by the present invention the liquid applied in the foregoing manner either contains adeveloping agent or dissolves such an agent upon application to the photosensitive element, and develops any latent image contained in the permeated portion of the photosensitive layer. The processing liquid may also cooperate with the materials permeated thereby to form in a stratum of the materials permeated a positive of the subject matter of the' latent image developed in the photosensitive layer.

It will be readily appreciated that the performance of photographic processing which involves the development of a silver halide emulsion by means of a single liquid application without recourse to baths of liquid is to be greatly desired,

particularly if this can be accomplished without requiring any subsequent liquid treatment of the materials subjected to the original processing. However, because the usual developing solution is a highly alkaline solution containing a developing agent which rapidly oxidizes in an alkaline environment, it will also be appreciated that under normal circumstances this type of application of a liquid processing agent not only develops a latent image in the photosensitive emulsion, but also provides in that emulsion materials which will develop unexposed or less exposed silver hal-" ide; particularly upon exposure of the emulsion tolig'ht; iMoreoven' if the development of the photosensitive emulsion is employed to produce the imagewise distribution of some component which tends to form a positive image in another layerjof material'associated with the emulsion, the tendency for continued development in the unexposed regions of the negative will render more critical thecontrcl of the time of formation of the positive image. More serious than this, however, in the latter case is that the developing agent which permeates the associated layer will, because of the oxidizable condition of the developing agent, tend upon" exposure to air to form undesirablestains in this associated layer which will adversely afiectwith time the pictorial quality or an image formed in said associated layer.

It is an object of the'present invention to improve proces'sesof' the foregoing type so as to permit the use'o'f a highly alkaline developing solution without the'aiorementioned disadvantages which would normally attend such use so that noafter treatment by a separate washing or other applicationof liquid is necessary to preserve the processed-photosensitive element for its intended function. According to'the present invention this-object isachieved by the presence in the material permeated by the processing liquid of a substance which prevents thereduction by the developing agent of the unexposed silver halide in the photosensitive layer and which elimi-. nates the stain-forming propensity of the devel-. oping solution. This substance is selected. from the class of materials which will hydrolyze in an alkalinesolution to consume alkali, and whose rate and amount of'hydrolysis is related to the alkalinity of the processing liquid and to the rate at which the developing agent of the liquid develops the latent image in the emulsion in such a way that there is no substantial diminution of the alkalinity of said solution. during the developing. of said latent image, and that shortly after or during the later stages of the development there is created in the permeated materials an environment of such reduced alkalinity as to prevent further appreciable oxidation of the developing agent. I p

Thenovel stabilizing or neutralizing agents for this purpose are preferably selected from the class of organic compounds which react in alkaline solution to consume alkali. These organic compounds are derivatives of organic acids, pref erably the carboxylic acids, and may, for example, be esters (including lactones), amides, anhydrides, aldehydes and imides, and these compounds in general 'showthe desired properties principally because an organicbond must be sevever, it is to be understood that the relatively water-insoluble organic compounds of this class are also within the scope of the present invention, being applicable for example in suitable non aqueous solvents.

The processes and products of. theinvention are. particularly useful in connection with processes wherein the silver halide layer is processed. while in superposed relation with another layer and wherein the processing liquid causes the.

formation in or on said other layer of a visible image. of the subject; matter of thedevelopedla.- tentv image. The twov layers may be. in substantial contactwith one another or may bespaced apart.- a short distance-by aseparating medium which permits ions and molecules to migrate freely between said layers during. the processing. A preferred form of transfer-process; isone wherein a print of the'latent image is formed by the transfer of the undeveloped silver halidefrom the photosensitive-layer. In such transfer processes thephotosensitivesilver halide-layeris permeated with a solution of a developin agent and a substance for forming a. soluble complex with silver halide. The latter ingredients are of such character and are contained. in'the solvent in such proportions that the developing agent. is capable of developing a latent imagein the photosensitive area while the complex-forming substance forms soluble complex with the undeveloped silver halide. A part at least of this complex is transported to a layer of material superposed with the photosensitive layer at or prior to the time of permeation of-said photosensitive layer; andthe silver of-th e-complex-isthere-pre cipitated to form animage-irr silver; whichi's the reverse orthe developed image in the photosensitivelayer;

The foregoing process may be performed by spreading a processing; agent between the silver halide and'other layer,; which processing agent contains a. suitable solvent and a suitable thi'cl'rening agent; such for example as a film-forming. high. molecular weight. polymer. When the. solvent has permeated the. photosensitive layer it contains the developing. agent and the. complex-forming. substance. in. solution, and one or both of thelatter ingredients may be dissolved. therein prior to. the spreading thereof, or may become dissolved therein. from one of said layers during the spreading.

The organic acid derivatives. which serve. as stablizing or neutralizin agents are. preferably distributed uniformly as measured in a planev parallel to the plane of the photosensitive layer in. or on one of the materials permeated by the processing layer, being located in. a position to readily contact and react with said liquid as it permeates the photosensitive layer and such permeable layer or layers as may be associated therewith. The stablizing agent may be applied to the photosensitive element or it may be contained in at least a portion of the thicknesstherefor, as for example in the photosensitive lay-e12, Where the processing liquid. is: spreadbetween the photosensitive element and another element as, for example, in a transfer process in which the other element serves as a print-rereiving layer, the stabilizing agent may be applied to one or both of said elements, but is most conveniently located on or just below the surface portions of said other element which are first permeated by the, liquid, during the. processing,

The class of compounds contemplated by the present invention are the organic compounds which are derivatives of carboxylic acids and which in an alkaline solution have a covalent bond severed to provide an acid component capable of reducing the alkalinity of the solution. The. compounds: are thus hydrolyzed in an alkaline. solution and consume alkali during the hydrolysis. The compounds have a rate of hydrolysis such that development of the emulsion is permitted to take place in the presence of the compounds Without being inhibited by a substantial reduction of the alkalinity of the. developing solution. However, the hydrolysis rate. is. such that after development has taken place there is a sufficient. diminution in. the alkalinity of the developing solution to appreciably inhibit further reducing action by the solution.

Preferred examples of organic compounds of this typeare the acid derivaties from the classconsisting of. the esters (including the'lactones), the amides, the anhydrides, the imides, and the aldehydes. These are compounds derived from the carboxylic acid of general formula.

; diethyl dv-tartrate a; hydroxybenzaldehyde, di-

methyl diactetyltartrate, dimethyl fumarate, dimethyl malate, dimethyl oxalate, "dimethyl tartrate, polyethyleneoxalate, benzoic anhydride, di-n-butyl oxalate, n-buty1 oxamate, di-n-butyl tartrate, trimethyl citrate, ethyl. cyanoacetate. ethyl N-B-hydroxyethyl oxamate, glucono delta lactone, glyceryl trismethyloxalate and cellulosemethyl oxalate.

In the performance of the. transfer processes the print-receiving element associated with the photosensitive element, either in a permanent or separable. arrangement, preferably" comprises a support: and may consist of a plurality of: layers or of but a single layer and preferably the material at one surface thereof is permeable to an aqueous solution of. a soluble silver complex. This permeable surface portion may be coated with or may be a coatin of. the novel stablizing agent. Preferably the support. for the print-receiving element is formedof. material such as paper, regenerated cellulose, polyvinyl alcohol, cellulose ethers such as methyl cellulose, ethyl cellulose and their derivatives such as aluminum fcarboxymethyl cellulose and hydroxyethyl cellulose, gums', and other resins, natural and synthetic, which form continuous films and which are preferably water permeable and relatively inert to alkalis,

'It is preferable where these stabilizing agents of the present invention are used in transfer processes, which involve photosensitive silver halide emulsions of the faster type, to provide in or on the print-receiving layer a silver precipitation initiator. This silver precipitation initiator may be any sulfur or selenium containing compound capable of releasing sulfide or selenide ions in an aqueous solution of a soluble silver complex and of forming the corresponding silver sulfide or selenidewith the silver of said complex, the latter acting as a nucleus for further silver precipitation. Examples of such compounds are: lead sulfide, cadmium sulfide, zinc sulfide, ferric sulfide, antimony sulfide, titanium sulfide, sodium sulfide, lanthanum sulfide, palladium sulfide, nickelous sulfide, lead selenide, zinc selenide, antimony selenide, nickelous selenide, dithiooxamide and its lead and zinc complexes, potassium dithiooxalate and lead complexes, and theoacetamide.

, The relatively insoluble heavy metal sulfides and selenides listed above are preferred, although more soluble sulfides and selenides such as those of the alkali earth metals and the alkali metals may also give satisfactory results, particularly if dispersed in a suitable inert pulverulent vehicle of the type hereinafter more fully described. Examples of these more soluble sulfides are sodium sulfide, potassium sulfide, sodium selenid and potassium selenide.

Preferred from the class of heavy metal sulfides and selenides are those whose solubility is not so low as to be below the solubility of'the corresponding sulfide or selenide of silver, and the best of these are salts whose solubility prod- ,ucts at a temperature of 20 C. vary between and 10- and specifically the sulfides of .zinc, cadmium and lead. A mixture of the salts of zinc, cadmium and lead is particularly desirable because the presence of the zinc sulfide, :which is white, and the presence of the cadmium sulfide, which is yellow, tend to produce a .minimum discoloration of the sheet while the lead sulfide provides the lead cations which even in very small concentration have been found to improve the contrast and density of a transfer print obtained from the fast photosensitive silver halide emulsions of the type containing a small quantity of silver iodide crystals, or at least some iodide ions in the photosensitive silver halide crystals thereof.

It is preferable to provide for the silver precipitation initiator a vehicle such as a layer of an inert, water-insoluble, water-adsorptive .pulverulent material. Examples of such materials are silica aerogel; diatomite, various forms of which are known as kieselguhr, diatomaceous earth, infusori-al earth, tripoli powder, and which are available under the name "celite and -super-fioss; a montmorillonite such the calcium montmorillonite available as fullers earth, or the sodium montmorillonite available as bentonite; a hydrous alkali silica such as magnesium silicate, or talc; finely ground glass; or a finely powdered wood such as wood flour.

The reduction in the alkalinity of the printuct possessing the features, properties and the relation of components, and the process involv-' ing the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference shouldbe had to the following detailed description taken in connection with the accompanying drawing, which is a diagrammatic enlarged sectional view illustrating the relation of elements during one stage of the performance of a transfer process, and showing as one of the elements an embodiment of the novel product of the invention, the thickness of the various materials being exaggerated.

A stage in the performance of a transfer process in accordance with the present invention is illustrated diagrammatically in the drawing wherein I ll represents a photosensitive element comprising a support Illa and a photosensitive silver halide emulsion layer lllb, l2 represents a support or carrier layer for the transfer print, and I4 represents a layer of relatively viscous processing liquid between element 10 and member l2.

Liquid layer I may be obtained by spreading the processing agent, for example in the manner disclosed in my copending application Serial No. 7,795, filed February 12, 1948, and the processing agent maybe one of the viscous film-forming processing agents disclosed in said copending application. It may comprise, for example, a developing agent such as hydroquinone, an alkali such as sodium hydroxide, a substance, such as sodium thiosulfate, for forming a soluble silver complex with unexposed silver halide, and a high molecular weight film-forming thickening agent such as sodium carboxymethyl cellulose. All these materials are preferably in aqueous solution. These various photographic reagents are preferably dissolved in the processing liquid prior to the spreading thereof, but they may be in part or wholly added to the processing liquid as it is spread between elements I!) and l 2, said reagents being so located on or adjacent the surface of one or both of said elements as to be dissolved by or otherwise interacted with the liquid agent when the latter wets said surface.. a

Photosensitive element It may be any of the commercially available photosensitive silver halide films, the latter term being understood to include paper-backed emulsions. The process of the present invention is particularly adapted to improve the results obtained when the higher speed photosensitive silver halide emulsions are used, such as the emulsion of the relatively highspeed orthochromatic films, e. g;,

arecontained in the same layer.

Eastman Kodak Verichrcme' film, having an ASA. speed rating of 0400'and an ASA exposure index rating in the daylight of 100, and Ansco Triple S Pan. The process also gives excellent results with the slower emulsions such as those of the printing and enlarging papers.

Element I2 preferably comprises a suitable support I20, for example of baryta paper, to the baryta-coated surface of which there is applied a layer I20, containing a silver precipitation initiator and over which there is-applied a further coating lZb containing or formed of the novel stabilizing agent of the invention. Although layers l2b and lZa are shown as separate and distinct layers, they may be intermingled to an appreciable extent and may permeate at least in part the surface portion of support 120. It is also within the scope of the. invention to interchange the order of the layers [2a and 121); that is, to apply the film of stabilizing agent to the base 120 and to apply over said film a coating containing the silver precipitation initiator. In another satisfactory form of member [2, the silver precipitation initiator and the stabilizing agent Where fast emulsions are not used or in case the permanence only of the print is important, its pictorial quality and color being of secondary consideration as where a writing is duplicated for the purpose of preserving a record of its subject matter, it is possible to dispense with the silver precipitation initiator.

When the foregoing liquid composition is spread or otherwise provided in a layer l4 between elements I and [2, the liquid thereof permeates photosensitive layer "lb and the developing agent acts to develop the latent image in said layer. Almost simultaneously with the development, the complex-forming substance, i. e., sodium thiosulfate, forms a soluble silver complex with the undeveloped silver halide. This silver complex is transported by the liquid of the processing agent to the film-forming material of layer 14, and thence to layers We and IE1), the silver precipitation initiator in layer 12a starting a vigorous controlled precipitation of the silver which causes the silver print to be formed predominantly in said layer.

Examples of processes for forming a positive image wherein the positive image of silver that is obtained is stabilized by means of the novel stabilizing agent of the invention, and examples of the novel elements useful as print-receiving materials in the performance of said processes are given below, but it is expressly understood that these examples are merely illustrative and that the invention is not limited to the materials or proportions set out therein.

Example 1 A processing agent is prepared which comprises? 8 The processing agent is prepared by dissolving the sodium carboxymethyl cellulose, for example that commercially available as Hercules 1362 medium viscosity type, in the water in a mixer at room temperature, and the solution is mixed therein for approximately one hour. Thereafter, the sodium sulfite, sodium hydroxide, sodium thiosulfate and citric acid are added to the solu tion, the addition being effected in an inert atmosphere, for example of nitrogen. Upon dissolution of these materials, the hydroquinone is added'and the solution is further mixed for an hour at approximately room temperature in a nonoxidizing atmosphere of nitrogen.

A print-receiving element [2 is formed by immersing the baryta-coated surface of a sheet of baryta paper in a mixture comprising:

Silica aerogel (Santocel C) g 300 1% solution of sodium sulfide cc 2800 Cadmium acetate g.... 30 Lead acetate g 1 Zinc nitrate g 30 Water 00....

for approximately ten seconds. As the sheet is withdrawn from said mixture, the excess of said mixture is removed from the surface by a bufier roll or squeegee. The sheet is then dried and washed in water for approximately one minute to remove most of the soluble salts therefrom, leaving thereon a layer I20. of silica aerogel containing predominantly metallic sulfides. The sheet is then dipped in a solution comprising 4.6% by weight of gum arabic and 10% by weight of dimethyloxalate to form on the silica aerogel layer a thin coating of gum arabic containing dimethyloxalate. To provide the gum arabic the commercially available product Arabol may be used. This is a water solution of gum arabic whose solid content varies between 57% and 61% and which has a visocity varying between 1500 and 1700 centipoises.

The processing agent is spread in a layer of approximately .002-.003" in thickness between the treated baryta surface of element l2 and the photosensitive silver halide emulsion E01) of a photosensitive film It. Emulsion lflb is a relatively high speed orthochromatic emulsion like the emulsion of Eastman Kodak Verichrome film, and has been exposed to predetermined subject matter to form therein a latentimage of said subject matter, support We for said emulsion being a white paper. The lamination formed by the spreading of the processing agent in a layer [4 between elements It and I2 is kept intact for approximately one-half to one and one-half minutes, preferably one minute, and at the end of this time element I2 is stripped from element It. Element I 2, when so stripped, carries a positive print in silver of the subject matter of the latent image in emulsion 10b. The sodium carboxymethyl cellulose of layer Hi adheres to coating 52b of element !2 and solidifies to form a film thereon. The print obtained in this manner has good color, density and other pictorial qualities, and is stable under vigorous heat and humidity tests.

Other materials may be substituted for those used in the foregoing process and the proportions maybe varied to an appreciable extent. For example, the film-forming material in the processing agent which imparts the desired viscosity to the latter may be any of the high molecular weight polymers which are stable to alkalis and which are soluble in aqueous alkaline solutions.

For example, such other plastics as hydroxyethyl cellulose, polyvinyl alcohol and the sodium salts of polymethacrylic acid and polyacrylic acid may be used. It is desirable that the plastic be contained in the agent in sufficient quantities to impart to the composition a viscosity in excess of 1000 centipoises at a temperature of approximately 24 C. Preferably the viscosities of the processing agent are of the order of 1000 to 200,000 centipoises.

Other developing agents may be used, for example'one of the following: p-aminophenol hydrochloride; bromohydroquinone; chlorohydroquinone; diaminophenol hydrochloride; diaminophenol dihydrochloride; toluhydroquinone; monomethyl-p-aminophenol sulfate; a mixture consisting by weight of one-half hydroquinone and one-half p-hydroxyphenyl amino-acetic acid; and a mixture consisting by weight of onefourth hydroquinone and three-fourths p-hydroxyphenylaminoacetic acid. a I To form the soluble silver complex such other complex-forming substances as sodium thiocyanate, ammonium thiocyanate and ammonia may be employed. Support [20 of element [2 may consist of gelatin, cellophane, polyvinyl alcohol, sodium alginate, and cellulose ethers such as methyl cellulose and their derivatives such as hydroxyethyl cellulose.

' EmampZe'Z The process of Example 1 may be carried out by usinginstead of the element 12 therein described a baryta sheet [2c which has layer lZa applied thereto in the same Way as in Example 1, but which then has its coated surface immersed in an 8% solution of dimethyloxalate in ethanol for approximately ten seconds. The

Sheet is then driedand used as described in Example 1.

" Examples For element I2 of Example 1 there is substituted a sheet of material formed by dipping a sheet of baryta paper in an aqueous solution comprising by weight 9% cadmium acetate, 18% zine nitrate and .3% lead acetate. After drying, the, sheet has coated thereon a mixture comprising:

Silica aerogel (Santocel C) g 300 1% aqueous solution of sodium sulfide cc 2800 Cadmium acetate g 30 Lead acetate g 1 Zinc nitrate"; -1 ..g 30 Water co 100 Water PP 100 G at n E Cadmium acetate g 25 Lead acetate g 1 When the sheet is again dry it is swabbed with a 3% solution of dimethyloxalate in ethanol.

I Examplcd The process of Example 1 is carried out with the print-receiving element I2 which is like the print-receiving element of Example 1 except that 2.1. 2- ?Qatins .121? thas abi ine a ent comprises a mixture of equal parts by volume of a 2% aqueous solution of gelatin and a 10% aqueous solution of dimethyloxalate.

Example 5 The process of Example 1 may be carried out with a print-receiving element 12 which is formed by providing in the same manner as in Example 1 on the baryta-coated surface of a sheet of baryta paper a coating of a mixture consisting of:

Water 0.. 5400 Cadmium a-r-Ptatp 1-1' 556 Lead acetat 2 18.6 Zinc nitrate g 556 Silica aerogel (Santocel C) g v7.20

3% aqueous solution sodium sulfide ..cc 1894 The sheet is dried and is then treated witha solution consisting of:

Water Arabol g 10. Ethyl oxamate g 8 Zinc nitrate e 4 by immersing in said solution for approximately ten seconds.

Example 6 A sheet of baryta paper has the baryta-coated 3% aqueous solution sodium sulfide cc 1650 The sheet is then dried and again immersed for approximately ten seconds in a mixture consist- Water Arabol g 150 Dimethyl tartrate g 300 Lead acetate e '70 Cadmium acetate g 50 Zinc acetate 2 40 The sheet thus produced may be used as element l2 in the process of Example 1.

Example 7 The baryta-coated surface of a sheet of baryta paperhascoated thereon a mixture of:

Silica aerogel g 300 1 aqueous solution sodium sulfide cc 2800' Cadmium acetate g 30 Lead acet 9 w 1. Zinc nitrate g 30. Water cc The sheet is then dried and dipped for approximatelythirty seconds in a solution consisting of;

Water 100 Dimethyl In g 20 Example 8 V A sheet, of baryta paper is processed inthe, same ,Wayas described in Example 7 except. that II for the water solution of dimethyl malate there is substituteda solution comprising:

Water cc 900 Arabol cc 100 Citric acid trimethyl ester -g 150 Emample 9 The baryta-coated surface of a sheet of baryta paper is dipped for one minute in a solution consisting of Water cc 100 Ethyl oxamate-"me"- g l Excess liquid is removed from the sheet and the sheet is then dried, for example, in an oven at a temperature of approximately 100 C. for about five minutes. The treated surface of the sheet is then rubbed with a mixture consisting of:

Silica aerogel g 300 1% aqueous solution sodium su1fide cc 2800 Cadmium acetate -1 g 30 Lead acetate g 1 Zinc nitrate -1 g 30 Water cc 100 Example 10 The baryta-coated surface of a sheet of baryta paper is dipped in a solution consisting of:

Ethanol cc 1000 Zinc nitrate g 120 Ethyl oxamate g 90 The treated surface of the sheet is then provided with a sulfide-containing coating in the same manner as the sheet of Example 9.

Example 11 The baryta-coated surface of a sheet of baryta paper is immersed in a mixture consisting of:

Water cc 1000 .Arabol cc 150 Dimethyl d-tartrate g 400 Lead acetate g '70 Cadmium acetate 'g- '50 Zinc acetate g 40 The sheet is then dried and there is applied over the layer containing the stabilizing ester a coating of the sulfide-containing mixture of Example 9 to give the finished print-receiving element [2.

Example 12 h The baryta-coated surface of a baryta paper is immersed for approximately thirty seconds in a solution consistingof a Water cc 1000 Dimethyl malate g 200 12 print-receiving elements formed in this man'neiv are the following:

Example 13 The baryta-coated surface of a baryta paper has rubbed thereon a mixture which is formed by adding- 2.5 grams of ethyl oxamate to 25 grams of a mixture consisting of Water .'CC 5400 Cadmium acetate g 556 Lead acetate g 18.6

Zinc nitrate g '556 Silica aerogel g 720 3% aqueous solution sodium sulfide cc 1894 Example 14 The baryta-coated surface of a baryta paper is immersed for approximately ten seconds in a mixture consisting of:

Water r fleece. 68 3% aqueous solution sodium su1fide cc =16 Silica aerogel g 4 Lead acetate g. "7. Cadmium acetate g.. 5.3 Zinc acetate g- 4 Dimethyl tartrate -1 30 A paper-backed photosensitive film l0. comprising as its emulsion IS?) a relatively high speed orthochromatic emulsion, like the emulsions of Eastman Kodak Verichrome film, is dipped in a solution consisting of -8 grams of 'dimethyl tartrate in cc. of water for approximately three seconds in the absence of light actinic to said emulsion. It is preferable to immerse two films in this manner and then run the two films in emulsion-to-emulsion engagement through a pair of pressure rollers. The two sheets of photosensitive film are then separated and dried.

A photosensitive sheet so processed is then exposed and the processing agent of Example 1 is spread between said sheet and a sheet of baryta paper in the manner described in Example .1, and upon separation of the photosensitive filmfrom the baryta paper after approximately a minute. the baryta paper carries a positive image of the latent image in said photosensitive'film.

Example 16 The pictorial quality of the positive image obtained in accordance with the process of Example 15 may be improved by coating the print-receiving element I2 with a silver precipitation initiator, as for example a sulfide-containing mixture of the type described in any of the preceding examples.

According to each of the foregoing examples there is. provided a photosensitive element or a print-receiving element which contains a stabilizing agent, and which, when used in accordance with the process described in detail in Example 1 in a photographic transfer process, gives a positive print which has improved keeping qualities. All of the prints formed in the presence '0'! the aesaosa organicxcompounds, which serve asstabilizing agents in the foregoing examples, are far more stable to severe heat and humidity tests than prints obtained-in exactly the same way without the stabilizing agent of the present invention.

Although all ofthe foregoing examples relate to transfer processes it is also possible, and may be very desirable in some'instances, to improve the keeping quality of adeveloped photosensitive emulsion so that the emulsion may be examined in its. developed condition for several minute in the light actinic to said emulsion. Ordinarily, of course, a developed negativ containing the developer in the unexposed region in concentration'capable of developing the exposed portion will have the unexposed portion quickly reduced if, the negative is exposed to light actinic to the emulsion. However, the presence of theenovel I stabilizing agent of the present invention in or on the photosensitive emulsion will stop this rapid fogging without inhibiting the developing, thereby making it possible to develop a negative by a single application of a developing solution and then without washing the negative orany subsequent treatment thereof to observe the latent image in light actinic to the emulsion. An example illustrative of this application of the invention is the following:

Example 17 This spreading may be accomplished as described in Example 1 between said film and another sheet material, such for example as a sheet of cellulose acetate. The two sheet materials are kept superposed in a darkroom'for approximately oneminute and are then separate'diat the end of this time the processing agent has developed the latent image in the film and the stabilizing ester stops further development sufiiciently so that the developed latent image may be observed under fluorescent light of approximately twenty footcandles for several minutes.

- Since certain changes may be made in the above product and process without departing from the scope of the inventionherein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted. as illustrative and not'in a limiting sense.

What is claimed is:

1. A photographic process for forming, by

I transfer, a positive print of a latent image contained in the silver halide emulsion of. a photosensitive element wherein a single application of liquid to said element is efiective .to give a finished print ,of improved stability, which process comprises the steps of bringing a relatively uniform layerwise distribution of a processing liquid into contact'with the photosensitive element so as to permeate said emulsion with said liquid, said layerwis distribution of processing liquid providing the entire mass of liquid for performing said process; causing said liquid to permeate said photosensitive element and a print-receiving ele-.i I ment superposed on said photosensitive element and providing, as reagents in said processing liquid, asilve'r halide developer, a silver halide solvent capable of forming transferable soluble sil= ver complexes with the unexposed silver halide of said emulsion, and an alkali, said developer being characterized by its propensity for oxidizing in an alkaline environment to produce stains; transferring from said emulsion layer, by imbibition, at least part of said soluble silver complexes onto a print-receiving layer supported on said printreceiving element; reducing to silver the silver ions of said soluble silver complexes upon said print-receiving layer to form an image in silver which is a positive of the subject matter of the latent image in the silver halide emulsion; and, at some stage of the process subsequent to the application of the processing liquid, introducing into the processing liquid an organic derivative of a carboxylic acid including in its linkage a covalent bond severable in an alkaline solution to free an acid component for reducing the alkalinity of said liquid, said organic compound being present in a permeated portion of one of said elements in a concentration sufiicient to appreciably reduce the alkalinity of said processing liquid and improve the stability of the transfer print.

2. The process of claim 1 wherein the processin liquid as brought into contact with said photosensitive layer contains in solution. the alkali and the developer and also contains a silver halide solvent. I

3. The process of claim 1 wherein the organic compound is an ester of a carboxylic acid.

4. A photographic process for forming, by transfer, a positive print of a latent image contained in the silver halide emulsion of a photosensitive element wherein a single application of liquid to said element is effective to give a finished print of improved stability. which process com-' prises the steps of spreading, in a layer between the photosensitive element and a print-receivingelement, all of the processing liquid for performing said process, which liquid includes, in solution, a silver halide developer, a silver halide solvent and an alkali and which, when spread, permeates the silver halide emulsion, said liquid developing the latent image in said emulsion and forming a positive print in silver upon said printreceiving element, the developer being characterized by its propensity for oxidizing in an-alkaline environment to produce stains; and, at some stage of the process subsequent to the spreading oi the processing liquid, introducing into the processing liquid an organic derivative of a carboxylic acid including in its linkage a covalent bond sev erable in an alkaline solution to free an acid component for reducing the alkalinity of said liquid, a surface portion of one of said elements being permeable to the processing liquid and formed of a material other than said organic compound and having said organic compound dispersed throughout the thickness thereof in a concentration sufficient to appreciably reduce the alkalinity of said processing liquid and improve the stability of thetransfer print. I

5. The process of claim 4 wherein the derivative ofa carboxylic acid is an ester.

- 6. The process f claim 4 wherein the derivative of a carboxylic acid is dimethyl oxalate.

' -7. The process of claim 4 wherein the derive-r tiveof a carboxylic acid is ethyl oxamate.

- 8. The processor claim 4 wherein the derivative of a carboxylic acid is dimethyl tartrate.

9. Th process of claim 4 wherein the derivative of a carboxylic acid is dimethyl malate.

10. The process of claim 4' wherein the derivative of a carboxylic acid is citric acid trimethyl ester.

11. A photographic process for forming, by transfer, a positive print of a latent image contained in the silver halide emulsion of a photosensitive element wherein a single application of liquid to said element is effective to give a finished print of improved stability, which process comprises the steps of bringing a relatively uniform layerwise distribution or a processing liquid into contact with the photosensitive element so as to permeate said emulsion with said liquid, said layerwise distribution of processing liquid providing the entire mass of liquid for performing said process causing saidliquid to permeate said photosensitive element and a print-receiving element superposed on said photosensitive element and providing, as reagents in said processing liquid, a silver halidedeveloper, a silver halide S01". vent capable of forming transferable soluble silver complexes with the unexposed silver halide of saidemulsion, and an alkali, said developer being characterized by its propensity for oxidizing in analkaline environment to produce stains; transferring from said emulsion layer, by imbibition, at least part of said soluble silver complexes onto a print-receiving layer supported on said print-receiving element; reducing to silver the silver ions of said soluble silver complexes upon said print-receiving layer to form an image in silver which is a positive of the subject matter of the latent image in the silver halide emulsion; and, at some stage of the process subsequent to the application of the processing liquid, introducing into the processing liquid an organic ester of a carboxylic acid including in its linkage a, covalent bond severable in an alkaline solution to free an acid component for reducing th alkalinity or said liquid, a surface portion of said print-receiving element being permeable to the processing liquid and formed of a material other than said organic ester and having said organic ester dispersed throughout the thickness thereof in a concentration sufilcient to appreciably reduce the alkalinity of said processing liquid and improve the stability of the transfer print.

12. A print-receiving element for having transfer prints formed thereon by precipitating the silver of a soluble silver complex brought into contact therewith, said element being substantially inert to light and comprising a support and a silver precipitation layer, one surface portion of said element, including said layer, being permeable to the ionic content of an aqueous solu--' tion of soluble silver complex, said layer comprising a macroscopically continuous matrix consisting essentially of submacroscopic particles of a water-insoluble, inorganic, chemically inert, adsorbent substance, said particles having a relatively low coefficient or absorption for light as compared to silver, said matrix having dispersed therethrough solid colloidal particles of a silver precipitating agent for aiding the reduction and precipitation of metallic silver from silver complex ions in the presence of a developing agent, said surface portion having distributed therethrough a stabilizing agent, said stabilizing agent being an organic derivative of a carboxylic acid which includes in its linkage a covalent bond severable in an alkaline solution to free an acid component for reducing the alkalinity of the solution.

13.' The product or claim 12 wherein said surface portion comprises a second layer other than said silver precipitation layer and said stabilizing agent is contained in said second layer.

14. The product of claim 13 wherein said silver precipitation layer is located between said second layer and said support.

15. The product of claim 12 wherein the organic derivative i an ester of a carboxylic acid and the particles of said water-insoluble, inorganic, chemically inert, adsorbent substance are particles of silica.

16. The product of claim 15 wherein the silver precipitating agent is a metallic sulfide whose solubility product at a temperatureof 20 C, is between 10 and 10 17. The product of claim 12 wherein the organic derivative is a compound from the clas consisting of diethyl oxalate, ethyl oxamate, diethyl d-tartrate, a hydroxy-benzaldehyde, dimethyl diacetyltartrate, dimethyl fumarate, dimethyl malate, dimethyl oxalate, dimethyl tartrate, polyethylene oxalate, benzoic anhydride, di-n-butyl oxalate, n-butyl oxamate, di-n-butyl tartrate, trimethyl citrate, ethyl cyanoacetate, ethyl N-B-hydroxyethyl oxamate, glucono delta lactone, glyceryl trismethyloxalate and cellulose methyl oxalate.

13. The product of claim 12 wherein the sur face portion of the print-receiving element throughout which the stabilizing agent is distributed is formed of materials which are different from said stabilizing agent and are permeated by thf latter, said stabilizing agent being an organic es er.

EDWIN H. LAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,930,140 Becker Oct. 10, 1933 2,019,718 Mannes et al Nov. 5, 1935 2,119,724: Stand June 7, 1938 2,139,767 Nadeau Dec. 13, 1938 2,171,609 Snyder Sept. 5, 1939 2,184,023 Sheppard Dec. 19, 1939 2,257,440 Wood Sept. 30, 1941 2,322,037 Lindquist June 15, 1943 2,341,583 Tuve Feb. 15, 1944 2,352,014 Rott June 20,1944 2,357,590 Jaffe Sept. 5, 1944 2,361,936 Gaspar Nov. 7, 1944 2,378,203 Fallesen June 12, 1945 2,399,981 Britt May 7, 1946 2,415,666 Weissberger Feb. 11, 1947 2,420,610 Mueller May 13, 1947 2,433,515 Jahod Dec. 30,1947, 2,494,055 Orkin Jan. 10, 1950 FOREIGN PATENTS I Number Country Date 382,320 Great Britain Oct. 27, 1932 392,424 Great Britain May 18, 19.33 826,812 France Jan. 12, 1938 873,507 France Mar. 23, 1942 879,995 France Mar. 19, 1943 OTHER REFERENCES Mees, The Theory of the Photographic .Process, published by the MacMillan Company, New York, 1942, pages 93-96.

Neblette Photographic Principles and Practice,- published by Van Nostrand Co., New York City, page 559-60. 

1. A PHOTOGRAPHIC PROCESS FOR FORMING, BY TRANSAFER, A POSITIVE PRINT OF A LATENT IMAGE CONTAINED IN THE SILVER HALIDE EMULSION OF A PHOTOSENSITIVE ELEMENT WHEREIN A SINGLE APPLICATION OF LIQUID TO SAID ELEMENT IS EFFECTIVE TO GIVE A FINISHED PRINT TO IMPROVED STABILITY, WHICH PROCESS COMPRISES THE STEPS OF BRINGING A RELATIVELY UNIFORM LAYERWISE DISTRIBUTION OF A PROCESSING LIQUID INTO CONTACT WITH THE PHOTOSENSITIVE ELEMENT SO AS TO PERMEATE SAID EMULSION WITH SAID LIQUID, SAID LAYERWISE DISTRIBUTION OF PROCESSING LIQUID PROVIDING THE ENTIRE MASS OF LIQUID FOR PERFORMING SAID PROCESS; CAUSING SAID LIQUID TO PERMEATE SAID PHOTOSENSITIVE ELEMENT AND A PRINT-RECEIVING ELEMENT SUPERPOSED ON SAID PHOTOSENSITIVE ELEMENT AND PROVIDING, AS REAGENTS IN SAID PROCESSING LIQUID, A SILVER HALIDE DEVELOPER, A SILVER HALIDE SOLVENT CAPABLE OF FORMING TRANSFERABLE SOLUBLE SILVER COMPLEXES WITH THE UNEXPOSED SILVER HALIDE OF SAID EMULSION, AND AN ALKALI, AND DEVELOPER BEING CHARACTERIZED BY ITS PROPENSITY FOR OXIDIZING IN AN ALKALINE ENVIRONMENT TO PRODUCE STAINS; TRANSFERRING FROM SAID EMULSION LAYER, BY IMBITITION, AT LEAST PART OF SAID SOLUBLE SILVER COMPLEXES ONTO A PRINT-RECEIVING LAYER SUPPORTED ON SAID PRINTRECEIVING ELEMENT; REDUCING TO SILVER THE SILVER IONS OF SAID SOLUBLE SILVER COMPLEXES UPON SAID PRINT-RECEIVING LAYER TO FORM AN IMAGE IN SILVER WHICH IS A POSITIVE OF THE SUBJECT MATTER OF THE LATENT IMAGE IN THE SILVER HALIDE EMULSION; AND, AT SOME STAGE OF THE PROCESS SUBSEQUENT TO THE APPLICATION OF THE PROCESSING LIQUID, INTRODUCING INTO THE PROCESSING LIQUID AN ORGANIC DERIVATION OF A CARBOXYLIC ACID INCLUDING IN ITS LINKAGE A COVALENT BOND SEVERABLE IN AN ALKALINE SOLUTION TO FREE AN ACID COMPONENT FOR REDUCING THE ALKALINITY OF SAID LIQUID, SAID ORGANIC COMPOUND BEING PRESENT IN A PERMEATED PORTION OF ONE OF SAID ELEMENTS IN A CONCENTRATION SUFFICIENT TO APPRECIABLY RE DUCE THE ALKALINITY OF SAID PROCESSING LIQUID AND IMPROVED THE STABILITY OF THE TRANSFER PRINT. 